Despite the proclamation of the French Consulate, the career of Saint-Sulpice seems to stagnate until 1803, when he is finally promoted to brigadier general.

With the proclamation of the Empire, Saint-Sulpice gets a position as Écuyer cavalcadour of the Empress Joséphine.

Named count of the Empire in 1808, he fights in most of the major engagements of the Fifth Coalition in 1809: Abensberg, Eckmühl, Ratisbon, Aspern-Essling and Wagram.

The next year, in March 1813, he is named governor of the castle of Fontainebleau but then is called to serve in the Grande Armée again for the War of the Sixth Coalition, fighting in Saxony.

In 1814, as the fighting continued, this time on French soil, Saint-Sulpice is assigned to serve under Marshal of the Empire Pierre Augereau, whose orders were to defend Lyon against the invading Allied armies.